1. Field of the Invention
The present invention relates to a field of material surface property modification, in particular, to a high-hardness metal-based/diamond composite coating and a high efficient preparation method thereof.
2. Description of Related Art
A metal ceramic takes advantages of both of a metal and a ceramic, it has low density, high hardness, high abrasion resistance, great thermal conductivity, and does not crack due to rapid temperature decrease or increase. The metal ceramic not only has metallic properties of robustness, high thermal conductivity and great thermal stability of the metal, but also has ceramic properties of high resistance to high temperature, corrosion and abrasion. The metal ceramic mainly includes a sintered aluminium (aluminium-aluminum oxide), a sintered beryllium (beryllium-beryllium oxide), a thoria dispersion (TD) nickel (nickel-thorium oxide) and so forth. A composite material is composed of one or several ceramic phases and metal phases or metal alloys, a generalized metal ceramic further comprises an alloy of a refractory composition, a rigid alloy or a diamond tool material that is bonded to a metal.
Preparation methods of a metal ceramic composite coating often being used include methods of thermal spraying, composite plating, laser in-situ synthesis, self-propagation combustion synthesis, spray welding, plasma transferred welding and so forth. For example, metal ceramic composite coatings of tungsten carbide (WC) base and chromium carbide (Cr3C2) base are successfully prepared by using a supersonic flame spraying, and have been applied in numbers of industrial fields.
Diamond serves as a highest-hardness natural material, a metal ceramic composite coating applying diamond as a strengthening phase has been widely studied both domestically and abroad, researchers in various countries have launched a large number of exploring researches on an aspect of preparing a metal-based/diamond composite coating.
When preparing the metal-based/diamond composite coating by utilizing methods of thermal spraying, spray welding, plasma transferred welding, laser cladding, self-propagation combustion synthesis and so forth, solid phase diamond particles react with a high temperature molten metal bonding phase, by which a thermal decomposition and dissolution are induced, so that the diamond particles are difficult to be maintained in the coating. Thus, the metal-based/diamond composite coating is not able to be prepared efficiently.
Although the chemical reaction at high temperature occurred in the above-mentioned method are avoided by methods of electroplating and electroless plating, which can maintain the diamond particles in the coating, and a volume content of diamond in the coating can reach 45%. However, a bonding at an interface between diamond and the binding phase is significantly deteriorated while the volume content of diamond in the coating is over 25%. A property of abrasion resistance of the coating is difficult to be improved, while the metal-based/diamond composite coating with thickness over 200 μm is difficult to be prepared by these methods, and a preparation efficiency thereof is low, technics thereof is complicated, and it may cause environment pollution, which make it difficult to be realized in industry.
A method of cold spraying, which has been developed in recent decades, is a new spraying technology realized by a collision between a substrate and low temperature solid particles at high speed that a severe plastic deformation is then occurred, so that a coating is deposited and formed. It avoids from changes of composition, texture and structure that may occur during high temperature deposition of thermal spraying, so that it is suitable for preparing coatings of temperature-sensitive materials (e.g. a nano-material, an amorphous material, and so forth), materials susceptible to oxidation (e.g. aluminum, copper, titanium and so forth) and materials susceptible to phase change (e.g. carbon-based composite materials). Although the metal-based/diamond composite coating can be prepared by the method of cold spraying, the composite coating is prepared mainly by a method of adding diamond to a metal substrate (e.g. aluminum) with relatively low hardness, that a high-hardness metal-based/diamond composite coating is difficult to be prepared, and a bonding between the diamond particles and the metal substrate is relatively weak, which easily results in detachment. In addition, a bonding mechanism between the cold-sprayed coating and the substrate is mainly a mechanical lock that a bonding strength between the coating and the substrate is relatively weak, which easily results in delamination of the coating.
As above, all of the current preparation methods of the metal-based/diamond composite coating have one or several problems as follows: (1) a thickness of the coating is low; (2) a content of diamond in the coating is low; (3) a bonding between diamond and the metallic phase in the coating is weak, which easily results in detachment; (4) the diamond particles in the coating are easily decomposed while being heated; (5) the bonding strength between the coating and the substrate is weak; (6) the metal-based/diamond composite coating is difficult to be prepared.